1. Field of the Invention
The present invention relates to a photographing optical lens system, and more particularly, to a photographing optical lens system used in electronic products for infrared band or visible light band.
2. Description of the Related Art
In recent years, the application of imaging lens systems is getting more and more popular, especially in computer webcams, automotive lens assemblies, surveillance cameras, and electronic game devices. Generally, the sensor of a general photographing camera is none other than CCD (Charge Coupled Device) or CMOS device (Complementary Metal Oxide Semiconductor device). Along with the advances in semiconductor manufacturing technology, the pixel size of sensors is reduced leading compact imaging lens systems to higher resolution. In the meantime, the demand for better image quality is also increased.
The wavelength range of visible light is generally between 400 and 700 nm, wherein the region of infrared light from 700 to 2000 nm is called the NIR (Near Infra-red, NIR) wavelength range, which is not detectable by the naked eyes. Since NIR has advantages of being less likely to be affected by interferences, lower cost and power consumption, and being highly secretive (less likely to be recognized by the naked eye), it is applied in many electronic technologies to develop various electronic products, such as remote control devices, infrared monitors and infrared detector systems. Also, the emerging motion capture technology applied in smart TV or motion sensing games also expands the application of compact imaging lens. The feature of these applications is by an infrared camera directly capturing the user's motion, the user takes control of the device intuitively; the experience of the motion sensing operation is elevated. Therefore, the demand for compact imaging lenses operated in the infrared wavelength range has increased; furthermore, lenses with wider viewing angles are even more favorable because they can extend the capturing range of the camera.
In view of this, an imaging lens structure applied in portable electronic devices is needed, which has a longer back focal length and the depression of the chief ray angle (CRA) for the better response performance of the sensor and has an efficient back focal length for disposing a filter element or a wavelength selector accordingly. On one hand, imaging lenses with this structure can be optimized for the requirement of the conventional photography (sufficient viewing angle, large aperture, image quality, etc.). On the other hand, lenses with this structure can be optimized for the requirement of the infrared photography, and designed for particular applications (such as the infrared imaging or motion capturing, etc.) at locations in low light conditions.